I made a page that checks the $_POST and see whether the password is correct. If it's correct, it'll display the page. If not, the user will be directed to another page.

1 thing is that after this page has been accessed, the user can use the back function on the browser to access the page again. If you need to see what I mean, my testing page is here: http://eddy05.sytes.net/wc3Replays/index.php and try the text field. The temporary password is abcxyz.

I need ideas on how to make the page expire after using it. Thank you very much.

When the admin keys in the correct password, he will be able to access the admin page. But after he uses the admin page, he is still able to access it using the BACK on the browser. my point is how to I make it expire so that even the BACK function won't work

Oh sorry... I would start a session that expires when the person choses Win or Lose... Unfortunately I have little experience with sessions and I'm no expert... but I'd do that and make the script change the password the person can't just log back in to do it anyway.